Fiber-optic communications transmit information from one place to another by sending a light stream through an optical fiber. This information-carrying light stream, which can be visible or invisible, and can be coherent or incoherent, and can be pulsed or can have a continuous amplitude, form an electromagnetic carrier wave which is modulated with the information. These modulated optical carrier waves can be referred to as optical carrier signals, or optical signals.
Multiplexing techniques, such as wavelength division multiplexing (WDM), can be used to transmit several different optical signals over a single optical fiber concurrently or simultaneously. Using WDM, each of the different optical signals has a different carrier wavelength, and one or more of the optical signals can be filtered from the other optical signals travelling through the optical fiber using a suitable optical filter mechanism. In some WDM applications, this optical filtering may not be required.
In multiplexed optical communications, it is sometimes desirable to add and/or drop an optical signal to an optical fiber through which one or more other optical signals are travelling. Typically, optical signals are added to an optical fiber using an optical multiplexing device. Such devices are referred to as optical add-drop multiplexers (OADM). OADM devices that include reconfigurable switches can also be referred to as reconfigurable optical add-drop multiplexers (ROADM). OADM devices which are not reconfigurable and where the add/drop functionality relies on fixed directivity and optical filtering can also be referred to as fixed optical add-drop multiplexers (FOADM).
An optical signal added to the optical fiber can, in some implementations, have parameters that are unknown to and/or inaccessible by the operator of the optical fiber and/or OADM. These parameters may include, for example, the wavelength of the optical signal, power of the optical signal, modulation format of the optical signal, or other parameters or characteristics. Such signals can be referred to as alien signals, alien wavelengths, or alien waves. In some implementations such signals can originate from a vendor different from the OADM vendor, or originate from equipment that is not under the control (or direct control) of the optical fiber and/or OADM. On the other hand, optical signals added to the optical fiber having parameters or characteristics, including those noted above, which are known and/or accessible by the operator of the optical fiber and/or OADM can be referred to as native signals, native wavelengths, or native waves. In some implementations, such native waves may originate from equipment that is under the control of the same vendor who controls the OADM equipment, for example.
An OADM can include one or more tributary input ports which are multiplexed and sent to a line output port (in the transmit/add direction). Tributary inputs can be single-wavelength (carrier/channel) sources, can be multi-carrier superchannels, or can be any combination of these (e.g., multiplexed before the OADM, where the multi-channel optical signal is then sent to a single tributary port of the OADM). The sources of these optical signals can be native to the line system (i.e., originate from or be under the control of the same OADM provider), can be alien wave sources, or can be a mix of both native and alien wave sources.
Because alien waves are not controlled by the operator of the optical fiber and/or OADM, insertion of, or changes in characteristics of, the alien wave during transmission can potentially disrupt the integrity of existing signals on the optical fiber (e.g., crosstalk, nonlinear impact, etc.), can result in failed operation, or can violate policies of the optical fiber network. Accordingly, it would be desirable to provide graceful turn-up, control, and/or maintenance for an alien wave. In some implementations, it may also be desirable to apply such graceful turn-up, control, and/or maintenance to native waves.